An atomic force microscope (AFM) scans over the surface of a sample. Typically, in the "contacting mode" of operation, a sharp tip is mounted on the end of a cantilever and the tip rides on the surface of a sample with an extremely light tracking force, on the order of 10.sup.-5 to 10.sup.-10 N. Profiles of the surface topography are obtained with extremely high resolution. Images showing the position of individual atoms are routinely obtained. In a second mode of operation, the tip is held a short distance, on the order of 5 to 500 Angstroms, from the surface of a sample and is deflected by various forces between the sample and the tip; such forces include electrostatic, magnetic, and van der Waals forces.
Atomic force microscopy is capable of imaging conductive as well as insulating surfaces with atomic resolution. Typical AFM's have a sensitivity of 0.1 Angstrom in the measurement of displacement, and a spring constant of about 1 Newton per meter (1 N/m). Further, the cantilever must be mounted so that the cantilever can approach and contact a sample.
Several methods of detecting the deflection of the cantilever are available which have sub-angstrom sensitivity, including vacuum tunneling, optical interferometry, optical beam deflection, capacitive and resistive techniques. One such technique is described in PCT Patent Document WO 9212398, "Piezoresistive Cantilever For Atomic Force Microscopy", published Jul. 23, 1992 (PCT Application No. 91US9759), which is incorporated herein by reference.
Scanning tunneling microscopes (STMs) are similar to AFMs, except that surface imaging is performed by detecting conductive properties of the surface being scanned.
While AFM/STM probe tips have been manufactured using semiconductor processing techniques in the past, the tips produced by those methods have tended to have a tip radius of at least 1000 angstroms, which is blunter than optimal.
It is an object of the present invention to provide a process for producing ultra-sharp AFM/STM probe tips.